Khorne Berzerkers
Khorne Berzerkers (languagefaggotry note: that should be Khornate Berzerkers, but "Khorne Berzerkers" is the official title) are Space Marines dedicated to Khorne, the god of blood, war, and fucking your shit up.
Most Khorne Berzerkers come from the World Eaters Traitor Legion. Their Primarch, Angron, decided that his most elite Marines should have partial lobotomies, just like himself. When this was done, the only emotion they could feel was RRRAAAAGGGGEEE. As the Horus Heresy dragged on, the World Eaters would eventually turn to the worship of Khorne, with the Berzerkers leading the way. Of course, they lost, fled to the Eye of Terror, and have spent the past 10,000 years worshipping Khorne the only way they know how: BATTLE, GLORIOUS BATTLE! Some renegades have joined them, but very few Space Marines are angry enough to keep up. They usually hang out in small squads to company to chapter size groups although the bigger formations are always temporary; there is too much RAGE going on in their minds to work together for long, because, after all, they are as likely to spill their comrades blood as an enemy's.
In game terms, they're basically regular Chaos Space Marines with Chainaxes and bolt pistols (which they hardly use but make good clubbing instruments). They also get Fearless and Furious Charge, as well as Marks of Khorne, which gives them Rage and Counter-Attack. This means that they absolutely butcher in melee... if they can get there. With a hefty price tag of 21 points per model, poor transport options (expensive Land Raider or assault-ramp-less Rhino), and the overall nerfing of melee in 6th Edition, it's very difficult to get them there. That's not to mention that regular Chaos Marines can be kitted out for close combat almost as well as the Berzerkers, and they are both cheaper and scoring. So, all in all, Berzerkers are losers this edition... but that's not really a change.